Patent Document 1 (shown below) shows a method for calculating an exhaust gas recirculation ratio using an intake air amount sensor which detects an intake air amount of an engine. The detected intake air amount sometimes deviates from an actual intake air amount due to differences in the characteristic of the intake air amount sensor and other factors. According to the method shown in Patent Document 1, calculation accuracy of the exhaust gas recirculation ratio decreases if there is such deviation in the detected intake air amount.
Patent Document 2 shows an air-fuel ratio control apparatus in which influence of the detection deviation of the intake air amount sensor is reduced. According to this control apparatus, an air-fuel ratio feedback control amount is calculated according to an air-fuel ratio (oxygen concentration) detected in the exhaust system of the engine, and a feedback control of the air-fuel ratio is performed using the air-fuel ratio feedback control amount. Further, in a high load engine operating condition where the throttle valve is substantially fully opened, an upper limit value for the detected value of the intake air amount sensor is changed based on the air-fuel ratio feedback control amount, which particularly prevents control accuracy of the air-fuel ratio from deteriorating due to influence of the intake air blowback caused by the intake air pulsation.